The soup can essentially be boiled down (haha, get it?) to just 3 ingredients: cauliflower, onion, and broth. Aside from that, you'll just need olive oil, salt + pepper. It will be absolutely delicious as is, but if you'd like, you can get more creative and throw in an endless variety of things. You can add garlic for oomph, and sherry vinegar for acid. You can add coconut milk and curry for Southeast Asian spin on the original. You can add Parmesan cheese and truffle oil for a cheesy, Italian feast. Have a little fun!
In a large pot, add 2 tablespoons of olive oil and turn the heat to medium-high. Add cauliflower florets and brown for about 5 minutes. Let the cauliflower get just a bit of color. Remove, set aside on a plate.
Add onion (and additional oil, as necessary) and sweat for 10-15 minutes until golden brown. Add the cauliflower back in. Season with salt, add 1 tablespoon of olive oil, all the broth, and cover. Let it come to a boil, then lower the heat to medium-low. Cook the soup for 30-45 minutes.
You want the cauliflower to come apart if you poke it. Add fresh-cracked pepper, then blend (I use a Vitamix). Taste for seasoning, and add salt if need be. Pour soup into bowls and garnish with desired toppings (I do sour cream, flaky salt, and chili flakes).